I just bought a DVI cable, so I can move the vga one to another computer. I have a CRT IBM p260, but when I have only DVI cable, there is no picture (I rebooted pc). Monitor is also set to input 2 (input 1 is vga).
I reattached vga cable (both cables were attached), so I executed nvidia settings, clicked detect display, and it was correctly recognised! However when I enable it (clone mode), there is no picture when switching to input 2!
I also tried other alignements (right of, left of, bottom....) nothing seems to work.

DVI cables can be used for digital, analog or both.
As these days costs are cut to the absolute minimum, there exist 3 different kinds of cable with only the necessary wires and pins for those functions.

A CRT monitor normally does not support digital connection and a DVI-D cable supports ONLY a digital connection. So this combination won't work.

As I said, in these days costs have to be cut to the extreme. An LCD monitor on a DVI connection does not use the analog signals, so the wires and pins for that are omitted in the DVI-D cable. Even those exist in a single-link and a dual-link version! The dual-link is only required for resolutions above 1920x1200 so the usual cable omits the extra link.